Junction temperature affects the performances of both light emitting diodes (LEDs) and laser diodes in many ways. For simplicity, this Application and the appended claims shall use the terms “LED” and “diode” to include both LEDs and laser diodes and the terms should be read as including both types of diodes without limiting the Application or the claims to just LEDs. The light output wavelength, spectrum, power magnitude, and diode reliability are all directly dependent on the junction temperature. Thus, the thermal design of a diode itself and the packaging in which a diode is encased become crucial to the overall performance of the device. The diode junction temperature is generated from three main components: the internal thermal resistance of the diode, the external thermal resistance (from the contact thermal resistance and the heat sink thermal resistance) and the ambient temperature. In a system with either high powered LED, the variable junction temperature of the LED is of paramount concern. The validation of thermal design and assembly requires the ability to measure junction temperature. The current method of testing the junction temperature is to test the temperature coefficient with forward voltage. The changing rate of the diode forward voltage with the junction temperature depends on the band gap and its series resistance. This requires separation of the effect of serial resistance, which is difficult to do. Therefore, a non-invasive, quick test of the junction temperature and its variation is a very interesting topic in all areas of the applications and research of the LEDs and lasers.
The present invention is an optical method of measuring junction temperature that leaves an LED or laser system operating intact. It is based on the peak wavelength of the LED and the shift of that peak wavelength with junction temperature changes. It is a very useful method for high powered LEDs and lasers and high powered diode systems.